An electrophotographic technology has been widely used in the field of copying machines and various printers because of its immediacy nature and high quality image.
Regarding an electrophotographic photoreceptor (hereinafter referred to as “photoreceptor”, as appropriate) which is the core of the electrophotographic technology, a photoreceptor based on an organic photoconductive material has been used because of its advantages such as no potential for pollution, easy formation of films and easy method of production.
As photoreceptors based on an organic photoconductive material are known a so-called monolayer type photoreceptor, in which a photoconductive fine powder is dispersed in a binder resin, and a lamination type photoreceptor, in which a charge generation layer and a charge transport layer are laminated. Lamination type photoreceptors have predominantly been developed and put to practical use, because high sensitivity photoreceptors can be obtained by combining a high efficiency charge generation material and a high efficiency charge transport material, the material can be selected from a wide range of materials enabling the realization of a safe photoreceptor, and a photosensitive layer can be formed easily by coating resulting in high productivity and low cost.
An electrophotographic photoreceptor is repeatedly used in an electrophotographic process such as charging, exposure, development, transfer, cleaning and charge removal, and therefore subjected to various stresses leading to deterioration. Such chemical and electrical deterioration includes: chemical damage caused to the photosensitive layer by strongly oxidizing ozone or NOx generated by a corona charger used as a charger; disruption of photosensitive layer composition by a carrier which is generated by image-exposing light or charge-removing light and which flows through the photosensitive layer, or by light from outside.
As another kind of deterioration, the following can be cited: mechanical deterioration on the surface of the photosensitive layer such as abrasion, flaw or peeling off of the film caused by rubbing with a cleaning blade or magnetic brush, or contact with a developer agent, transfer part member or paper. Such damage on the surface of the photosensitive layer tends to become apparent on the image, impairing the image quality directly, and this is an important factor in determining the life span of the photosensitive receptor. Therefore, in order to develop a long-life photoreceptor, improvement in mechanical strength as well as electrical and chemical durability is desired.
In the case of a general photoreceptor having no functional layer such as surface protective layer, it is a photosensitive layer which is exposed to such a load. A photosensitive layer usually consists of a binder resin and a photoconductive material. It is the binder resin which substantially determines its strength. However, as the amount of the photoconductive material to be doped is considerably large, sufficient mechanical strength has not been secured by the previously known technique.
As a binder resin of the photosensitive layer, the following can be used: thermoplastic resins and various thermosetting resins including polymethylmethacrylate, polystyrene, vinyl polymer such as polyvinyl chloride, their copolymers, polycarbonate, polyester, polysulfone, phenoxy, epoxy and silicone resins. Of these binder resins, polycarbonate resin is comparatively superior in performance and various kinds of polycarbonate resins have been developed and put to practical use (for example, refer to Patent Documents 1 to 4).
On the other hand, a technology on an electrophotographic photoreceptor has been disclosed in which a polyarylate resin, commercially available under the trade name of “U-polymer”, is used as a binder resin, wherein sensitivity has been claimed to be excellent in comparison with a polycarbonate resin (for example, refer to Patent Document 5).
Further, a technology has been disclosed in which a polyarylate resin, based on a bivalent phenol component of specific structure, is used as a binder resin, wherein solution stability at the time of production of the photoreceptor is known to be improved, and its mechanical strength, especially abrasion resistance, is known to be excellent. (For example, refer to Patent Documents 6 and 7).    [Patent Document 1] Japanese Patent Laid-Open Publication No. Sho 50-98332    [Patent Document 2] Japanese Patent Laid-Open Publication No. Sho 59-71057    [Patent Document 3] Japanese Patent Laid-Open Publication No. Sho 59-184251    [Patent Document 4] Japanese Patent Application No. Hei 5-21478    [Patent Document 5] Japanese Patent Laid-Open Publication No. Sho 56-135844    [Patent Document 6] Japanese Patent Laid-Open Publication No. Hei 3-6567    [Patent Document 7] Japanese Patent Laid-Open Publication No. Hei 10-288845